Crossflow Timming Question

[oscar boy]

I have a 94 115 HP Johnson that has been reciently rebuilt. The place I ordered my parts from in Flordia suggested I set the timming at 24 deg. instead of 28 deg. for the break in period. He also said the motor would last longer if I left it a 24 deg.<br />The motor is set at 24 deg now and will turn 5800 to 6000 rpm depending on which propeller I have on the boat. The boat is runnning 40 to 43 mph wot. At 4000 to 4200 rpm the boat runs 30 mph. which is the speed I usually run.<br />I am not interested in high speeds, but would like to know if there is any advantage to increasing the timming to 24 deg. I am happy with the performance of the motor as it is now, and have about 18 hours on the motor.<br />thanks

 

[rabidfish]

Re: Crossflow Timming Question

Setting the timming lower can help prevent detonation if you run hard alot.<br /><br />It may cost a little acceleration, but you may not notice it.

 

[oscar boy]

Re: Crossflow Timming Question

Thanks for your reply Rabidfish.<br /><br />Guess timming isn't something many on the forum have much experience with.

 

[Dhadley]

Re: Crossflow Timming Question

Why did you have to rebuild the motor?

 

[oscar boy]

Re: Crossflow Timming Question

Motor carboned up under the rings and caused the rings to break.

 

[rodbolt]

Re: Crossflow Timming Question

me I have never set timing in my life

 

[Dhadley]

Re: Crossflow Timming Question

Timing? We dont need no timing!!<br /><br />Seriously, if the motor broke rings before its probably going to need some adjusting on the set up. If the motor isnt capable of the proper rpms it will build extra combustion heat. That promotes coking and eventually a ring will break. Most likely on the starboard bank.<br /><br />If you chose to run the motor in a "lugging" situation you may indeed want to leave the timing at 24. That might help delay the coking but eventually it will happen again.<br /><br />If we get the motor set up properly, 5800+ with an average load, you can set the timing per the factory at 28. And youll probably never have to worry about coking.

 

[oscar boy]

Re: Crossflow Timming Question

At WOT the motor is turning 5800 to 6000 rpm with 17" pitch prop. At that rpm the boat is running 40 to 43 mph. The motor is trimmed up and sounds likes it may be trimmed a bit high. This speed is faster than I like to run. The prop that was on the boat before was a 19" pitch.<br /> I know a higher rpm the timming needs to be advanced more, and it seem at 4000 rpm which is the speed I run most, less advance might be needed.<br /> The reason is ask, Is the man I bought My parts from said to set it at 24 deg for the break in period and for longer motor life leave it set there.<br /> The reason I posted the question was to see in anyone had the same view, or perhaps the guy I bought the parts from dosen't know what he is talking about.

 

[Dhadley]

Re: Crossflow Timming Question

Your set up seems real good. personally I like to set the timing where it belongs. Try this (if your sure the timing is at 24 at wot) -- make a run with the boat long enough to establish a good baseline on speed and rpm as it is now. Then advance the timing stop screw 2 turns. That will advance you from 24 to 26 degrees. Make the same run. If you see an improvement, advance it to 28 degrees. It probably wont show any gains so go back to 26. If it does improve, leave it at 28.<br /><br />This is all provided, as mentioned, that youre sure its at 24 now at 6000 rpm.

 

[oscar boy]

Re: Crossflow Timming Question

Thanks for the suggestion I'll do that and let you know the results. It may be afew weeks before I have time, lots of rain and too many thigs competing for my time.<br /><br />I appreciate your help.

 

[Dhadley]

Re: Crossflow Timming Question

Sounds good. just make darn sure where the timing is now at 6000 before you advance it. Pistons dont like it if it goes too far.

 

[oscar boy]

Re: Crossflow Timming Question

I'll do a test run and check the timming before I make any changes, and go from there.<br /><br />Thanks again for your reply

 

[Dhadley]

Re: Crossflow Timming Question

Thats the best way!<br /><br />Good luck! Let us know what you find.